Processes are primarily known for the production of .alpha.-DL-tocopherol.
.alpha.-Tocopherol and the derivatives thereof are significant as feedstuff additives, anti-oxidants, agents to stimulate circulation of the blood, agents to reduce cell aging and for related applications.
According to the prior art, trimethylhydroquinone (TMHQ) is generally used as the starting material, which is reacted with isophytol using various catalyst systems. (DE-OS 4243464=U.S. Pat. No. 5,523,420, DE-OS 19603142, EP 0694 541). Once the reaction is complete, the product must then be completely acetylated in order to obtain, for example, conventional commercial, storage-stable vitamin E acetate. A feature common to all these processes is that they do not directly give rise to tocopherol acetate, the conventional commercial, storage-stable form of vitamin E.
Attempts have also been made to synthesize tocopherols by reacting trimethylhydroquinone ester as the educt with isophytol.
FR-A 2 259822 (DE-OS 2 404621) relates to the use of diacetylated trimethylhydroquinone.
However, the condensation described therein with isophytol in the presence of a solid acid results in a yield of only approx. 41% .alpha.-DL-tocopherol and does not give rise to the corresponding esters.
DE-OS 2 160 103 (=U.S. Pat. No. 3,789,086) describes the condensation of trimethylhydroquinone monoacetate with isophytol.
Using Fe(II)Cl.sub.2 and hydrochloric acid with simultaneous separation of the water of reaction gives rise to only small quantities of the .alpha.-tocopherol acetate and it is necessary to perform post-acetylation with amine catalysis and addition of superstoichiometric quantities of acetic anhydride.
According to JP-OS 51-80859 (15.sup.th July 1976), trimethylhydroquinone or the ester thereof is reacted with isophytol in the presence of zinc chloride.
In accordance with the stated object, the reaction gives rise to .alpha.-tocopherol at temperatures of greater than 100.degree. C.